What does high-frequency mean?

In electrical engineering, frequencies above 10 kHz are described as high-frequency. But for power tools this term is commonly used to describe all frequencies above the standard mains frequency of 50/60 Hz. Modern high-frequency power tools usually operate at a frequency of 300 Hz.
But why is the current from the socket at a higher frequency? One reason is the need for enhanced performance. By increasing the frequency, you can achieve a higher speed. The motor’s output power increases as a direct proportion of increased frequency: at 300 Hz, performance is six times better because the frequency is six times greater than at 50 Hz. The frequency converters required for this, that bring the power up to the higher frequency, are connected to the national three-phase grid.

There are also many benefits to using high-frequency power tools in an industrial setting:

  • There are also many benefits to using high-frequency power tools in an industrial setting. the productivity increase is extremely noticeable, thanks to the increased power, ideal speeds, constant speed stability even under load and the associated very high grinding performance.
  • Tool wear is minimised.
  • FEIN high-frequency power tools are also designed for maximum load capacity and with minimum maintenance in mind. This results in longer service lives, shorter downtimes and reduced maintenance and repairs.
  • In industrial continuous use, for example in multi-shift operation, choosing FEIN high-frequency technology also delivers better cost-effectiveness.

Stationary high-frequency systems.

If several workstations have to be fitted into a given space, we would recommend a permanent installation with one larger frequency converter and permanent cables. FEIN KSR frequency converters are asynchronous-synchronous frequency converters. The output voltage only deviates by ± 1% from the set idling voltage, even under load. The converters are short-circuit-proof. It is standard practice to connect several KSR converters of similar types and sizes in parallel.
The FEIN frequency converters feature protection class IP 54. They are virtually maintenance-free. As a guide, the maintenance interval for the ball bearings is approximately 20,000 operating hours. When installing the frequency converters, the site simply requires good ventilation vibrations during operation. FEIN recommends fitting anti-vibration buffers to minimise (max. air temperature + 40° C).

High Frequency Grinding


Technical data MO 83 - 7,5 KSR MO 83 - 11 KSR MO 83 - 15 KSR MO 83 - 20 KSR MO 83 - 25 KSR MO 83 - 30 KSR MO 83 - 45 KSR
Voltage on secondary side 200 V 200 V 200 V 200 V 200 V 200 V 200 V
output power 7,5 kVA 11 kVA 15 kVA 20 kVA 25 kVA 30 kVA 45 kVA
Motor 8 kVA 11,6 kVA 15 kVA 20 kVA 24 kVA 28 kVA 41 kVA
Motor current (400 V) 16 A 21,4 A 26,6 A 34,2 A 44,2 A 49,4 A 75,1 A
Power consumption 11,1 kVA 14,9 kVA 18,5 kVA 23,8 kVA 30,7 kVA 34,4 kVA 52,1 kVA
Idling power 1,1 kVA 1,4 kVA 2,4 kVA 2,8 kVA 3,3 kVA 3,7 kVA 5,4 kVA
Scope of services factor 0,8 cos φ 0,8 cos φ 0,8 cos φ 0,8 cos φ 0,8 cos φ 0,8 cos φ 0,8 cos φ
Weight 75 kg 110 kg 164 kg 176 kg 200 kg 240 kg 360 kg
Length x width x height 794 x 258 x 360 mm 844 x 258 x 360 mm 1058 x 310 x 416 mm 1058 x 310 x 416 mm 1058 x 310 x 416 mm 1058 x 310 x 416 mm 1252 x 348 x 463 mm

Maximum Performance

Maximum performance in continuous use.

Higher frequency, constant speeds, higher performance. The superior tool concept of FEIN high-frequency power tools makes them particularly well suited to use in metalwork, for heavy-duty grinding and continuous use when roughing-down or cutting under the toughest working conditions.

  • Thanks to design-related measures like induction motors and the fact that wearing power-transmitting parts are not used, FEIN high-frequency power tools satisfy very high robustness andservice life requirements.
  • They have power reserves, on average a good 100 % higher than normal.
  • In everyday use, this translates into constant speed across the entire load range. For efficient working with a high grinding performance and lower levels of disc wear.
  • The FEIN high-frequency range includes a wide selection of angle grinders and straight grinders for tradespeople and professional users in industry.
    FEIN high-frequency power tools can also be used as portable devices on the construction site or on stationary grinding stations.

  Comparison of characteristic curves depending on the power of different tool types

High-frequency cost-effective working.

In terms of investment, energy and maintenance costs, high-frequency power tools are much more cost-effective than comparable standard-frequency or pneumatic tools. The sample calculations below show a comparison of the systems.

High frequency compared with standard frequency.

A higher frequency means a higher speed which increases the motor’s output power. Increasing the frequency from 50 Hz to 300 Hz therefore increasing power sixfold while retaining the same size and weight. The optimum power/weight ratio is reached at 300 Hz. Outstanding speed stability over the entire load range ensures optimum peripheral speeds which impacts positively on grinding performance, productivity and an appreciable reduction in grinding disc wear.
The induction motors of the high-frequency power tools with squirrel cage rotors feature no wearing power-transmitting parts. They don’t need powerful ventilation, just surface ventilation, which allows them to be fully encapsulated and gives the motors complete dust protection. High-frequency tools have simple structures, making them easy, fast and cheap to maintain. Stationary frequency converters require virtually no service – with the exception of ball bearing maintenance (roughly every 20,000 operating hours).

High frequency compared with standard frequency.

High frequency compared with pneumatic system.

The power distribution system for high-frequency power tools has virtually no energy losses, while with pneumatic systems the heat produced when compressing air results in greater energy losses. In reality, an additional 10 to 20 % more energy is needed due to leaks – if the systems are poorly maintained, this figure may even rise to 30% and above. The performance of the pneumatic motors also depends on the condition of their components, which are subject to wear (for example, cylinder, rotor, thrust washers, flaps). This translates into continuous performance losses which in turn results in falling efficiency and rising energy consumption. Highfrequency power tools on the other hand continue to perform with full power after many hours of work: the performance of the robust induction motors remains constant at all times – regardless of wear.

High frequency compared with pneumatic system.



Durable Power Tools

A durable system.

In many areas of industry and manual trades where tools are expected to deliver maximum performance permanently, FEIN high frequency tools prove to be superior. Compared with pneumatic tools and also power tools with a universal motor, their design brings them a number of benefits which deliver huge potential for cutting costs and therefore makes them the most sensible choice in many areas of metalwork. Both the construction and quality of the products have been designed to very high standards. The FEIN quality you would expect of a product made in Germany and more than 50 years of experience in developing and producing high-frequency power tools guarantees absolute reliability and a superior service life for industrial continuous use under the toughest conditions.

Durable Power


By increasing the frequency, you can achieve a higher motor speed. The motor’s output power increases in direct proportion to frequency.


No ingress of aggressive, abrasive swarf thanks to the encapsulated, dust-proof motor with surface cooling.


No rotating windings or powertransmitting elements such as carbon brushes or collectors, resulting in minimal wear.


Designed for extreme conditions of use, with high mechanical stability for unique load capacity for continuous industrial use.


Significantly longer tool service life and maximum grinding power from great speed stability even under load.